1. Field of the Invention
The present invention relates to a light-source lamp unit that appropriately works as a light source for an optical apparatus such as a projection-type display apparatus which is capable of employing different types of light source. The present invention also relates to a light-source device having such a light-source lamp unit and a projection-type display apparatus having such a light-source device.
2. Description of the Related Art
Projection-type display apparatuses capable of projecting an enlarged image from a personal computer have been actively studied and developed. Such a projection-type display apparatus modulates an output light from a light-source lamp using a light valve such as a liquid-crystal display panel based on an image signal, and enlarges and projects the modulated light image on a projection screen through a projection lens.
Used as a light-source lamp for the projection-type display apparatus are a metal halide lamp, a xenon lamp, and a high-pressure mercury lamp. These light-source lamps emit a relatively stable light for a few thousand hours, but if they are used longer, the life of the lamp will expire, the quantity of light drops, and light intensity varies depending on wavelength, possibly degrading color balance. When the life of the lamp actually expires, a projected image is darkened and the color balance drops degrading image quality. To preclude such problems, it is necessary to replace the lamp before its life expires.
To avoid continuously using a lamp into its life-expired state, a mechanism for automatically warning that the lamp is approaching its expiration of life or a mechanism for forcibly blocking the use of the lamp expired have been proposed. For example, Japanese Unexamined Patent Publication Nos. 4-5622, 4-163584, 4-250437, and 4-323531 disclose such mechanisms.
In these mechanisms, the operation time count of the lamp should be measured, and when the lamp is replaced with a new one, the replacement has to be automatically detected to clear the time count value. Some mechanisms have been proposed for sensing automatically that an expendable item such as a lamp is replaced with a new one, wherein a fuse, attached to the expendable item such as a lamp, is employed such that it melts at the replacement of the item and the opening of the fuse by the melt is electrically detected to determine whether the expendable item is a new one. For example, mechanisms using such a fuse are proposed in Japanese Unexamined Patent Publication Nos. 4-144754 and 6-89287.
The technique proposed in the above disclosures assumes that the same type of lamp is usually used as the light source. In a diversity of optical apparatus, there will be times when lamps of different types and different output powers need to be selectively used depending on operational environments.
In the projection-type display apparatus, for example, the brightness of a projected image is subject to its upper limit when the same light-source lamp is used. Depending on operational environment, the projected image lacks brightness. For example, when a metal halide lamp is used as a light-source lamp, the display apparatus is designed to selectively employ lamps of 180 W and 100 W, and when a brighter projected image is needed, a 180 W lamp may be used.
With lamps of different characteristics, for example, of different output power, each lamp needs to be driven at driving condition appropriate to the characteristics of the lamp, and to this end, lamp drive and control circuits need to be replaced to match each lamp type. Such an method is not only inconvenient but also costly to run.
The 180 W metal halide lamp has a service life of 1000 hours or so while a low-power 100 W metal halide lamp has a longer service life of 6000 hours. In the projection-type display apparatus permitting lamps of different characteristics, if the techniques described in the above disclosures apply as they are, the service life of each lamp cannot be correctly determined and a display advising a lamp replacement cannot be presented in a timely manner, because the lamps are different from each other in service life. For example, when a 180 W metal halide lamp is replaced with a 100 W metal halide lamp after a fixed period of time of use, the operation time count for the current lamp is added to the operation time count for the first lamp, and then, the 100 W metal halide lamp is erroneously determined as a life-expired one, though it is not. Furthermore, when the 180 W metal halide lamp is replaced with the 100 W metal halide lamp, the 100 W metal halide lamp is sensed as a new one, and the operation time count of the 180 W metal halide lamp until then is cleared, and even if the same 180 lamp is used again, the operation time count is not considered in counting, and the opening of the lamp may suddenly take place before the determination of life expiration.
The lamps vary in color balance depending on their type, and a projected image of the projection-type display apparatus is maintained at its proper condition by the use of a lamp having a color balance that matches the type of the projected image and the operational environment. To this end, an arrangement is preferably provided to permit lamps of different types to be selectively used. Even in such an arrangement, however, the lamps of different types vary in life and lamp output power, and it is necessary to drive each lamp according to a driving condition appropriate to the lamp and to determine the life of the lamp depending on its type. The techniques proposed in the above disclosures fail to perform these functions.
A lamp drawing near to the end of life suffers a drop in luminance, and the luminance of the light source suddenly rises when the lamp is replaced with a new one. As a result, the projection-type display apparatus presents a sudden rise in brightness in the projected image, and a user has to manually adjust luminance each time the lamp is replaced. Manually adjusting the luminance of the light source at each lamp replacement is troublesome and inconvenient.